For many years so called "friction tape" was used to hold small parts together, as an electrically insulating material to cover otherwise exposed electrical conductors, especially at wire-to-wire connections, and for many other purposes. Friction tape was made by impregnating a woven cloth material with a black, nondrying adhesive material. The tape was normally supplied in rolls of varying widths from which supply the desired length of tape would be withdrawn for use and easily cut or simply torn off. If dispensers were used, they were more for convenience in holding a roll or rolls of tape than for severing it as desired because the tape was so easily torn.
With the coming of the plastic age, plastic film of various compositions were and are employed in place of the woven fabric and one or both sides of the plastic film were coated with a pressure sensitive adhesive material. This product had the advantages of lower cost and also greater conformability with the contours of the surfaces to which the tape was applied. A disadvantage of the plastic pressure sensitive tape has been the greater difficulty of tearing the portion of the tape to be used from the supply roll dispenser which holds the supply roll and usually includes means for severing the tape as required. Rolls of the tape for electrical, mechanical and securing means were also supplied for use without the cutter-dispensers, a knife, scissors, or other tool that might be available at the moment being used to cut the tape. Attempts to tear a piece of pressure sensitive plastic adhesive tape, as had theretofore been done with friction tape, frequently meant only frustration. Except when applied by an experienced person as a quick snap exerted at the very edge of the tape, tensile forces tended only to stretch instead of rupturing the tape.
As used herein, the term "plastic tape" means a flexible strip of plastic film having an essentially constant width and initially a length which is a large positive multiple of its width. The term "tear-off tape" means tape which may be readily severed by manual manipulation without the use of any cutting tool.
The object of the present invention is to provide pressure sensitive plastic adhesive tape which can be easily torn to separate a desired length for use from the supply roll. More specifically, a tape of this kind is provided with closely spaced points of weakness along at least one of the edges of the tape these points being formed by tiny notches shallow cuts or tears which have the effect of concentrating the forces of tension applied at the edge of the tape at one of the tiny notches at which point of weakness the tear is started. Once started, completion of the tear proceeds easily. The tiny notches or shallow cuts or tears may be provided inexpensively by diverse means some of which are described hereinbelow by way of example.
In one aspect of the invention, a simple and inexpensive method of producing a roll of easily severable tape from a normal roll of normal pressure sensitive plastic adhesive tape is described. This may be done by applying a sharp grit sandpaper to the side surface of a normal roll of plastic tape and working the surface by abrading it with appropriate pressure in haphazard directions to scratch the surface formed by the collective edges of the convolutions of the tape forming the roll and thus introducing the multiplicity of closely spaced points of weakness as required by the easy tear-off of the tape of the invention.